Low impurity hydrazine

ABSTRACT

This invention relates to the purification of aqueous solutions of hydrazine and lower alkyl hydrazines to remove impurities. More particularly, it relates to the removal of sodium and other cations, chloride, carbonate and other anions from aqueous solutions of such hydrazines. The product solutions have, at most, extremely low limits of ionic impurities.

United States Patent Rigsby 51 Mar. 28, 1972 [54] LOW IMPURITY HYDRAZINE [72] Inventor: James G. Rigsby, Lake Charles, La.

[73] Assignee: Olin Corporation, New Haven, Conn.

[22] Filed: Dec. 2, 1969 [21] Appl. No.: 881,589

FOREIGN PATENTS OR APPLICATIONS 1,060,065 2/1967 Great Britain ..23/ 190 Primary Examiner-Oscar R. Vertiz Assistant Examiner-Hoke S. Miller Anomey-Gordon D. Byrkit, Donald F. Clements and Thomas P. ODay ABSTRACT This invention relates to the purification of aqueous solutions of hydrazine and lower alkyl hydrazines to remove impurities.

More particularly, it relates to the removal of sodium and other cations, chloride, carbonate and other anions from aqueous solutions of such hydrazines. The product solutions have, at most, extremely low limits of ionic impurities.

6 Claims, No Drawings LOW IMPURITY HYDRAZINE The commonly used Raschig synthesis of hydrazines reacts aqueous sodium hypochlorite with aqueous ammonia to form chloramine which reacts further with ammonia to form hydrazine according to equations l and (2):

NaOCl NH;,---* NH CI NaOH 1 When primary or secondary lower alkyl amines are substituted for ammonia in equation (2), the corresponding lower alkyl substituted hydrazines result.

In addition to synthesis reactions (1) and (2), side reactions occur to some extent as represented by equations (3) and (4):

By-product sodium chloride is formed according to equation (2) in a 1:1 molar ratio with the desired hydrazine product and ammonium chloride is formed in lesser proportions according to equations (3) and (4). These chlorides and any other relatively non-volatile by-products are removed by flashing the more volatile hydrazine and water from the relatively non-volatile by-products.

The hydrazines are concentrated and refined by distillation and/or extraction.

In spite of these process operations, aqueous hydrazine solutions, containing up to 65 percent of N H the N I'I 'I-I O hydrate, still contain minor amounts of ionic impurities, particularly sodium chloride. These amounts, in parts per million (p.p.m.), are not of consequence for many uses of hydrazine but they are objectionable for certain uses, for example, in electroplating and in nuclear-powered electric generating plants. For these and other purposes, it is required that aqueous hydrazine solutions be provided which contain preferably p.p.m. NaCl or, at least, below p.p.m.

One object of this invention is to provide a method for the purification of aqueous solutions of hydrazines. More particularly, an object of this invention is to provide a method for the removal therefrom of these small amounts of ionic impurities. A further object is to provide purified aqueous hydrazine uniquely suitable for certain uses. Other and further objects appear in the following description.

The objects of this invention are achieved by contacting the aqueous hydrazine solution first with the hydrazinium form of strongly acidic cation exchange resins and then with the hydroxyl form of strongly basic anion exchange resins and separating the treated aqueous hydrazine from the resins. In a further embodiment of the invention, cyclic treatment of aqueous hydrazine solutions is contemplated in which a plurality of bodies of the cation and anion exchange resins are alternatley used and regenerated to provide continuous treatment of the hydrazine solutions with or without automatic control of the treating and regenerating portions of the cycle.

It is known, for example, in U.S. Pat. No. 2,789,036 to remove anions such as chlorate, sulfate, chloride and ferrite from aqueous caustic soda by contacting the caustic solution with an anion exchange resin. U.S. Pat. No. 2,991,156 discloses removing iron from aqueous caustic soda by contacting with certain polyvinylbenzyl sulfonium halide resins. Glycerol has been purified by passage through successive beds of regenerated cation and anion exchange resins as described in Ind. Eng. Chem., vol. 43, pp. 1065-70 (1951). In addition, hydrazines have been purified as described in U.S. Pat. No. 3,458,283 by exchanging hydrazinium salt solutions with a cation exchange resin to adsorb hydrazinium ions on said resin and recovering the purified hydrazine by eluting the hydrazinium resin with aqueous caustic soda. It appears that great care would be required in this patented process to use exactly the stoichiometric quantity of caustic soda and to contact all of the hydrazinium resin with all of the aqueous caustic soda allowing ample time for complete interaction since any excess of the caustic soda or any unreacted caustic soda used in the elution must contaminate the product with ionic impurities.

Aqueous hydrazines are strongly basic and are strong reducing agents which interact with many ion exchange resins. Some of the resins are degraded, substantially inactivated or rendered inoperative by such interaction. For example, aqueous hydrazine, reacting with the hydrogen form of active cation exchange resins, generates quantities of heat. Proper design and control is required to dissipate such heat to prevent melting certain resins. Other problems arise which are solved by the process of the present invention.

In operation, fresh or acid-regenerated cation exchange resin is first converted to the hydrazinium form of resin under conditions providing dissipation of heat at an adequate rate to avoid damaging the resin. With certain resins, this operation is suitably performed in the tower or container for holding the bed of resin as it is to be used in de-cationizing the aqueous hydrazine depending on ambient air to dissipate the heat liberated. In other instances, this preliminary treatment is suitably carried out in a separate vessel equipped with jackets and/or cooling coils to remove the heat. Similarly, regeneration of the exhausted or partly spent resin with acid requires suitable provision for heat control.

The strongly basic anion exchange resins suitable for use according to the present invention are usually initially in the hydroxyl form but, if not, they are converted to the hydroxyl form by treatment with aqueous alkali, preferably caustic soda. The spent or partially exhausted resins are also regenerated with aqueous caustic soda. Suitable precautions are taken to dissipate the heat liberated in both of these processes.

In continuous operation, the aqueous hydrazine flows through a bed of the cation exchange resin initially in the hydrazinium form and then through a bed of the anion exchange resin initially in the hydroxyl form until the resin beds are partially spent and passage of ions through the beds is imminent. The flow of aqueous hydrazine is switched to a parallel pair of towers and flows first through a bed of regenerated cation exchange resin and then through a bed of regenerated anion exchange resin. While the aqueous hydrazine is flowing through the second pair of towers, the resins in the first pair of towers is suitably regenerated. The cation exchange resin bed is washed by flowing soft or deionized water through it to remove aqueous hydrazine, then aqueous acid, preferably hydrochloric acid, about I to 10 percent HCl is passed through the bed until cations other than hydrogen are substantially removed and then water is again passed through the bed until chloride ions are substantially removed. Similarly, the anion exchange resin bed in regenerated by flowing soft of deionized water therethrough to remove aqueous hydrazine, then aqueous alkali, preferably caustic soda, about 1 to I0 percent is passed through the bed until anions other than hydroxyl are substantially removed and then water is again passed through the bed until sodium ions are substantially removed. The regenerated beds are suitably covered with soft or deionized water until used. The aqueous hydrazine washed from both beds is recycled to storage of impure hydrazine for further treatment or, if too dilute, to the hydrazine plant for concentration.

The reactions involved in the process of the present invention, including regeneration reactions, using R nonstoichiometrically to represent the resins, are as follows:

CATION EXCHANGE RESIN Pretreatment: R.l-I N H R.N H Deionization: R.N H Na R.Na N l-l, H Regeneration: R.Na I-ICl R.I-I. NaCl ANION EXCHANGE RESIN Pretreatment: R.Cl NaOI-l R.Cl-I NaCl Deionization: R.Cl-I +Cl" R.Cl OH Regeneration: R.Cl NaOI-I R.Cl-l +-NaCl The process of this invention is useful in purifying aqueous solutions of hydrazine and of lower alkyl hydrazines having one to four carbons per alkyl group and from one to two alkyl groups per nitrogen, whether made by the Raschig process or otherwise. Examples of such alkyl substituted hydrazines indeionized is appropriately cooled as necessary to avoiddamage to the resin. Otherwise, temperatures of operation are not critical and are suitably as low as F.

Besides sodium and chloride ions, minor amounts of other cations and anions are effectively removed by the process of the present invention. In the product, lithium, potassium, copper, iron, chromium, calcium, barium and strontium cations, if present, are reduced to negligible amounts. Similarly, carbonate, bromide, iodide, nitrate and other anions, if present, are reduced to negligible amounts.

The cation exchange resins are of the strong acid type, for example, sulfonic acids and salts. These include sulfonated polystyrene resins, sulfonated phenol-fonnaldehyde resins and other sulfonic acid types. The anion exchange resins are of the strongly basic type, for example amine or quaternary salts. These include polystyrene-substituted quaternary ammonium salts, hydroxyalkyl quaternary type resins and other strongly basic types.

The method of this invention is useful for purification of strong aqueous solutions up to 65 percent N 11, or higher. Dilute solutions having 5 percent or less of N 11, are also effectively purified when costs can be economically justified. It is preferred to purify hydrazine solutions having from about to 65 percent N 11 EXAMPLE I An aqueous solution of hydrazine, containing 15 percent N,l-I and 225 p.p.m. NaCl was passed through a bed of sulfonated cation exchange resin and the effluent was passed through a bed of strongly basic anion exchange resin. The chloride content of the effluent was reduced to p.p.m.

EXAMPLE II EXAMPLE lll Aqueous hydrazine containing 13.9 percent N,H., and 72 p.p.m. N aCl was passed successively through beds of strongly acidic cation exchange resin and strongly basic anion exchange resin. The cation resin bed was 2 inches in diameter, 36 inches deep and contained 0.0654 cu. ft. of bed. The anion resin bed was 2 inches in diameter, 48 inches deep and contained 0.0874 cu. ft. of bed. The aqueous hydrazine flow averaged 245 milliliters per minute and the total throughput was 94.9 gallons. The effluent, tested at intervals, averaged 6 p.p.m. NaCl. No change appeared in the hydrazine concentratron.

EXAMPLE IV Using fresh resins, the procedure of Example III was repeated. The feed of aqueous hydrazine contained 73 to 83 p.p.m. NaCl. A total of 75.12 gallons of aqueous hydrazine was passed through the beds. The product averaged 10.6 p.p.m. NaCl.

' EXAMPLE V Using fresh resins, the procedure of Example I was repeated. The feed of aqueous hydrazine contained 50 to 78 p.p.m. NaCl. The effluent, amounting to 62.52 gallons, averaged 11.6 p.p.m. NaCl.

EXAMPLE VI Using fresh resins, the procedure of Example 111 was repeated. The feed of aqueous hydrazine contained 50 to 52 p.p.m. NaCl. The effluent, amounting to 93.18 gallons, averaged 6.6 p.p.m. NaCl.

EXAMPLE VII 139 cc./min. with 9 percent hydrochloric acid and rinsing for 60 minutes with 139 cc./min. of deionized water. The bed was left covered with deionized water until placed in use.

The anion resin bed had a diameter of 4.7 cm., a depth of 70 cm. and a volume of 1,215 cc. It was prepared by backwashing the column upwards for 12 minutes with 353 cc./min. of deionized water, regenerating for minutes using 41.3 cc./min. of 4 percent aqueous caustic soda and rinsing for 160 minutes with 81.4 ccJmin. of deionized water. The bed was left covered with deionized water until placed in use.

Aqueous hydrazine containing 35.5 percent N,H 96 p.p.m. Na ion and 165 CI ion was passed serially through the bed of cation exchange resin and the bed of anion exchange resin at a rate of 140 cc. per minute. Samples taken every 30 minutes showed 0 sodium and averaged 10.2 p.p.m. chloride.

EXAMPLE VIII The cation resin bed used in Example VII was backwashed upwards for 12 minutes using 353 cc./min. of tap water, regenerated for 30 minutes using 139 cc./min. of 9 percent BC] and rinsed for 70 minutes with 158 cc./min. of deionized water. The bed was left covered with deionized water until used.

The anion resin bed used in Example VII was backwashed for 15 minutes using 230 cc./min. of tap water, regenerated for 80 minutes using 50 cc./min. of 4 percent aqueous caustic soda and rinsed for 210 minutes using 87 cc./min. of deionized water. The bed was left covered with deionized water until used.

Each column was purged with nitrogen for 30 minutes to remove air and water. Then an aqueous solution of hydrazine containing 64.4 percent N,l-I.,, p.p.m. of Na ion and p.p.m. of Cl ion was passed successively through the resin beds at 2.42 cc./min. After 3 hours, the effluent showed 0.02 p.p.m. Na ion and 0.8 p.p.m. Cl ion.

What is claimed is:

1. Method of removing ionic impurities from an aqueous solution of hydrazine by contacting said solution first with the hydrazinium form of a strongly acidic cation exchange resin, separating the first treated aqueous hydrazine from said cation exchange resin, contacting said first treated aqueous hydrazine with the hydroxyl form of a strongly basic anion exchange resin and separating from said anion exchange resin the second treated aqueous hydrazine.

2. Method as claimed in claim 1 in which said cation exchange resin is a sulfonated polystyrene resin.

3. Method as claimed in claim 1 in which said anion exchange resin is a polystyrene-substituted quaternary ammonium resin.

4. Method as claimed in claim 1 in which said aqueous solution of hydrazine contains from 10 to 65 percent N 11 5. Method as claimed in claim 1 in which said contacting is maintained at temperatures between 0 and 300 F.

said resins, regenerating said first beds of resins while said flow of aqueous hydrazine passes through said second beds of resins, transferring said flow of impure aqueous hydrazine to the regenerated first beds and repeating the cycle.

i U i i i 

2. Method as claimed in claim 1 in which said cation exchange resin is a sulfonated polystyrene resin.
 3. Method as claimed in claim 1 in which said anion exchange resin is a polystyrene-substituted quaternary ammonium resin.
 4. Method as claimed in claim 1 in which said aqueous solution of hydrazine contains from 10 to 65 percent N2H4.
 5. Method as claimed in claim 1 in which said contacting is maintained at temperatures between 0* and 300* F.
 6. Method as claimed in claim 1 in which a flow of impure aqueous hydrazine is maintained through a first bed of said cation exchange resin and then through a first bed of said anion exchange resin until elution of ions from said beds of ion exchange resin reaches a predetermined limit, transferring said flow of impure aqueous hydrazine through second beds of said resins, regenerating said first beds of resins while said flow of aqueous hydrazine passes through said second beds of resins, transferring said flow of impure aqueous hydrazine to the regenerated first beds and repeating the cycle. 